/**
 * Copyright (C) 2014 Stratio (http://stratio.com)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.stratio.decision.api.partitioner;

/*
 *
 * Copyright 2006-2008 Makoto YUI
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Contributors:
 *     Makoto YUI - initial implementation
 */
//package xbird.util.hashes;

/**
 * Produces 32-bit hash for hash table lookup.
 *
 * <pre>
 * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
 *
 * You can use this free for any purpose.  It's in the public domain.
 * It has no warranty.
 * </pre>
 *
 * @see <a href="http://burtleburtle.net/bob/c/lookup3.c">lookup3.c</a>
 * @see <a href="http://www.ddj.com/184410284">Hash Functions (and how this function compares to others such as CRC, MD?, etc</a>
 * @see <a href="http://burtleburtle.net/bob/hash/doobs.html">Has update on the Dr. Dobbs Article</a>
 */
public final class JenkinsHash {
    private static long INT_MASK = 0x00000000ffffffffL;
    private static long BYTE_MASK = 0x00000000000000ffL;

    public JenkinsHash() {}

    public static int hash32(final byte[] key, final int initval) {
        return hash32(key, key.length, initval);
    }

    /**
     * taken from  hashlittle() -- hash a variable-length key into a 32-bit value
     *
     * @param key the key (the unaligned variable-length array of bytes)
     * @param nbytes number of bytes to include in hash
     * @param initval can be any integer value
     * @return a 32-bit value.  Every bit of the key affects every bit of the
     * return value.  Two keys differing by one or two bits will have totally
     * different hash values.
     *
     * <p>The best hash table sizes are powers of 2.  There is no need to do mod
     * a prime (mod is sooo slow!).  If you need less than 32 bits, use a bitmask.
     * For example, if you need only 10 bits, do
     * <code>h = (h &amp; hashmask(10));</code>
     * In which case, the hash table should have hashsize(10) elements.
     *
     * <p>If you are hashing n strings byte[][] k, do it like this:
     * for (int i = 0, h = 0; i &lt; n; ++i) h = hash( k[i], h);
     *
     * <p>By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this
     * code any way you wish, private, educational, or commercial.  It's free.
     *
     * <p>Use for hash table lookup, or anything where one collision in 2^^32 is
     * acceptable.  Do NOT use for cryptographic purposes.
     */
    public static int hash32(final byte[] key, final int nbytes, final int initval) {
        int length = nbytes;
        long a, b, c; // We use longs because we don't have unsigned ints
        a = b = c = (0x00000000deadbeefL + length + initval) & INT_MASK;
        int offset = 0;
        for(; length > 12; offset += 12, length -= 12) {
            a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK;
            a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
            a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
            a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
            b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK;
            b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
            b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
            b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
            c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK;
            c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
            c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
            c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;

            /*
             * mix -- mix 3 32-bit values reversibly.
             * This is reversible, so any information in (a,b,c) before mix() is
             * still in (a,b,c) after mix().
             *
             * If four pairs of (a,b,c) inputs are run through mix(), or through
             * mix() in reverse, there are at least 32 bits of the output that
             * are sometimes the same for one pair and different for another pair.
             *
             * This was tested for:
             * - pairs that differed by one bit, by two bits, in any combination
             *   of top bits of (a,b,c), or in any combination of bottom bits of
             *   (a,b,c).
             * - "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
             *   the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
             *    is commonly produced by subtraction) look like a single 1-bit
             *    difference.
             * - the base values were pseudorandom, all zero but one bit set, or
             *   all zero plus a counter that starts at zero.
             *
             * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
             * satisfy this are
             *     4  6  8 16 19  4
             *     9 15  3 18 27 15
             *    14  9  3  7 17  3
             * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing for
             * "differ" defined as + with a one-bit base and a two-bit delta.  I
             * used http://burtleburtle.net/bob/hash/avalanche.html to choose
             * the operations, constants, and arrangements of the variables.
             *
             * This does not achieve avalanche.  There are input bits of (a,b,c)
             * that fail to affect some output bits of (a,b,c), especially of a.
             * The most thoroughly mixed value is c, but it doesn't really even
             * achieve avalanche in c.
             *
             * This allows some parallelism.  Read-after-writes are good at doubling
             * the number of bits affected, so the goal of mixing pulls in the
             * opposite direction as the goal of parallelism.  I did what I could.
             * Rotates seem to cost as much as shifts on every machine I could lay
             * my hands on, and rotates are much kinder to the top and bottom bits,
             * so I used rotates.
             *
             * #define mix(a,b,c) \
             * { \
             *   a -= c;  a ^= rot(c, 4);  c += b; \
             *   b -= a;  b ^= rot(a, 6);  a += c; \
             *   c -= b;  c ^= rot(b, 8);  b += a; \
             *   a -= c;  a ^= rot(c,16);  c += b; \
             *   b -= a;  b ^= rot(a,19);  a += c; \
             *   c -= b;  c ^= rot(b, 4);  b += a; \
             * }
             *
             * mix(a,b,c);
             */
            a = (a - c) & INT_MASK;
            a ^= rot(c, 4);
            c = (c + b) & INT_MASK;
            b = (b - a) & INT_MASK;
            b ^= rot(a, 6);
            a = (a + c) & INT_MASK;
            c = (c - b) & INT_MASK;
            c ^= rot(b, 8);
            b = (b + a) & INT_MASK;
            a = (a - c) & INT_MASK;
            a ^= rot(c, 16);
            c = (c + b) & INT_MASK;
            b = (b - a) & INT_MASK;
            b ^= rot(a, 19);
            a = (a + c) & INT_MASK;
            c = (c - b) & INT_MASK;
            c ^= rot(b, 4);
            b = (b + a) & INT_MASK;
        }

        //-------------------------------- last block: affect all 32 bits of (c)
        switch(length) { // all the case statements fall through
        case 12:
            c = (c + (((key[offset + 11] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
        case 11:
            c = (c + (((key[offset + 10] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
        case 10:
            c = (c + (((key[offset + 9] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
        case 9:
            c = (c + (key[offset + 8] & BYTE_MASK)) & INT_MASK;
        case 8:
            b = (b + (((key[offset + 7] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
        case 7:
            b = (b + (((key[offset + 6] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
        case 6:
            b = (b + (((key[offset + 5] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
        case 5:
            b = (b + (key[offset + 4] & BYTE_MASK)) & INT_MASK;
        case 4:
            a = (a + (((key[offset + 3] & BYTE_MASK) << 24) & INT_MASK)) & INT_MASK;
        case 3:
            a = (a + (((key[offset + 2] & BYTE_MASK) << 16) & INT_MASK)) & INT_MASK;
        case 2:
            a = (a + (((key[offset + 1] & BYTE_MASK) << 8) & INT_MASK)) & INT_MASK;
        case 1:
            a = (a + (key[offset + 0] & BYTE_MASK)) & INT_MASK;
            break;
        case 0:
            return (int) (c & INT_MASK);
        }
        /*
         * final -- final mixing of 3 32-bit values (a,b,c) into c
         *
         * Pairs of (a,b,c) values differing in only a few bits will usually
         * produce values of c that look totally different.  This was tested for
         * - pairs that differed by one bit, by two bits, in any combination
         *   of top bits of (a,b,c), or in any combination of bottom bits of
         *   (a,b,c).
         *
         * - "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
         *   the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
         *   is commonly produced by subtraction) look like a single 1-bit
         *   difference.
         *
         * - the base values were pseudorandom, all zero but one bit set, or
         *   all zero plus a counter that starts at zero.
         *
         * These constants passed:
         *   14 11 25 16 4 14 24
         *   12 14 25 16 4 14 24
         * and these came close:
         *    4  8 15 26 3 22 24
         *   10  8 15 26 3 22 24
         *   11  8 15 26 3 22 24
         *
         * #define final(a,b,c) \
         * {
         *   c ^= b; c -= rot(b,14); \
         *   a ^= c; a -= rot(c,11); \
         *   b ^= a; b -= rot(a,25); \
         *   c ^= b; c -= rot(b,16); \
         *   a ^= c; a -= rot(c,4);  \
         *   b ^= a; b -= rot(a,14); \
         *   c ^= b; c -= rot(b,24); \
         * }
         *
         */
        c ^= b;
        c = (c - rot(b, 14)) & INT_MASK;
        a ^= c;
        a = (a - rot(c, 11)) & INT_MASK;
        b ^= a;
        b = (b - rot(a, 25)) & INT_MASK;
        c ^= b;
        c = (c - rot(b, 16)) & INT_MASK;
        a ^= c;
        a = (a - rot(c, 4)) & INT_MASK;
        b ^= a;
        b = (b - rot(a, 14)) & INT_MASK;
        c ^= b;
        c = (c - rot(b, 24)) & INT_MASK;

        return (int) (c & INT_MASK);
    }

    private static long rot(final long val, final int pos) {
        return ((Integer.rotateLeft((int) (val & INT_MASK), pos)) & INT_MASK);
    }

    /*
     * --------------------------------------------------------------------
     * hash() -- hash a variable-length key into a 64-bit value k : the key (the
     * unaligned variable-length array of bytes) level : can be any 8-byte value
     * Returns a 64-bit value. Every bit of the key affects every bit of the
     * return value. No funnels. Every 1-bit and 2-bit delta achieves avalanche.
     * About 41+5len instructions.
     *
     * The best hash table sizes are powers of 2. There is no need to do mod a
     * prime (mod is sooo slow!). If you need less than 64 bits, use a bitmask.
     * For example, if you need only 10 bits, do h = (h & hashmask(10)); In
     * which case, the hash table should have hashsize(10) elements.
     *
     * If you are hashing n strings (ub1 **)k, do it like this: for (i=0, h=0;
     * i<n; ++i) h = hash( k[i], len[i], h);
     *
     * By Bob Jenkins, Jan 4 1997. bob_jenkins@burtleburtle.net. You may use
     * this code any way you wish, private, educational, or commercial, but I
     * would appreciate if you give me credit.
     *
     * See http://burtleburtle.net/bob/hash/evahash.html Use for hash table
     * lookup, or anything where one collision in 2^^64 is acceptable. Do NOT
     * use for cryptographic purposes.
     * --------------------------------------------------------------------
     */
    public static long hash64(final byte[] k, final long initval) {
        /* Set up the internal state */
        long a = initval;
        long b = initval;
        /* the golden ratio; an arbitrary value */
        long c = 0x9e3779b97f4a7c13L;
        int len = k.length;

        /*---------------------------------------- handle most of the key */
        int i = 0;
        while(len >= 24) {
            a += gatherLongLE(k, i);
            b += gatherLongLE(k, i + 8);
            c += gatherLongLE(k, i + 16);

            /* mix64(a, b, c); */
            a -= b;
            a -= c;
            a ^= (c >> 43);
            b -= c;
            b -= a;
            b ^= (a << 9);
            c -= a;
            c -= b;
            c ^= (b >> 8);
            a -= b;
            a -= c;
            a ^= (c >> 38);
            b -= c;
            b -= a;
            b ^= (a << 23);
            c -= a;
            c -= b;
            c ^= (b >> 5);
            a -= b;
            a -= c;
            a ^= (c >> 35);
            b -= c;
            b -= a;
            b ^= (a << 49);
            c -= a;
            c -= b;
            c ^= (b >> 11);
            a -= b;
            a -= c;
            a ^= (c >> 12);
            b -= c;
            b -= a;
            b ^= (a << 18);
            c -= a;
            c -= b;
            c ^= (b >> 22);
            /* mix64(a, b, c); */

            i += 24;
            len -= 24;
        }

        /*------------------------------------- handle the last 23 bytes */
        c += k.length;

        if(len > 0) {
            if(len >= 8) {
                a += gatherLongLE(k, i);
                if(len >= 16) {
                    b += gatherLongLE(k, i + 8);
                    // this is bit asymmetric; LSB is reserved for length (see
                    // above)
                    if(len > 16) {
                        c += (gatherPartialLongLE(k, i + 16, len - 16) << 8);
                    }
                } else if(len > 8) {
                    b += gatherPartialLongLE(k, i + 8, len - 8);
                }
            } else {
                a += gatherPartialLongLE(k, i, len);
            }
        }

        /* mix64(a, b, c); */
        a -= b;
        a -= c;
        a ^= (c >> 43);
        b -= c;
        b -= a;
        b ^= (a << 9);
        c -= a;
        c -= b;
        c ^= (b >> 8);
        a -= b;
        a -= c;
        a ^= (c >> 38);
        b -= c;
        b -= a;
        b ^= (a << 23);
        c -= a;
        c -= b;
        c ^= (b >> 5);
        a -= b;
        a -= c;
        a ^= (c >> 35);
        b -= c;
        b -= a;
        b ^= (a << 49);
        c -= a;
        c -= b;
        c ^= (b >> 11);
        a -= b;
        a -= c;
        a ^= (c >> 12);
        b -= c;
        b -= a;
        b ^= (a << 18);
        c -= a;
        c -= b;
        c ^= (b >> 22);
        /* mix64(a, b, c); */

        return c;
    }

    /** perform unsigned extension of int to long */
    private static final long uintToLong(final int i) {
        long l = (long) i;
        return (l << 32) >>> 32;
    }

    /** gather a long from the specified index into the byte array */
    private static final long gatherLongLE(final byte[] data, final int index) {
        int i1 = gatherIntLE(data, index);
        long l2 = gatherIntLE(data, index + 4);

        return uintToLong(i1) | (l2 << 32);
    }

    /**
     * gather a partial long from the specified index using the specified number
     * of bytes into the byte array
     */
    private static final long gatherPartialLongLE(final byte[] data, final int index, final int available) {
        if(available >= 4) {
            int i = gatherIntLE(data, index);
            long l = uintToLong(i);

            int left = available - 4;

            if(left == 0) {
                return l;
            }

            int i2 = gatherPartialIntLE(data, index + 4, left);

            l <<= (left << 3);
            l |= (long) i2;

            return l;
        } else {
            return (long) gatherPartialIntLE(data, index, available);
        }
    }

    /** gather an int from the specified index into the byte array */
    private static final int gatherIntLE(final byte[] data, final int index) {
        int i = data[index] & 0xFF;

        i |= (data[index + 1] & 0xFF) << 8;
        i |= (data[index + 2] & 0xFF) << 16;
        i |= (data[index + 3] << 24);

        return i;
    }

    /**
     * gather a partial int from the specified index using the specified number
     * of bytes into the byte array
     */
    private static final int gatherPartialIntLE(final byte[] data, final int index, final int available) {
        int i = data[index] & 0xFF;

        if(available > 1) {
            i |= (data[index + 1] & 0xFF) << 8;
            if(available > 2) {
                i |= (data[index + 2] & 0xFF) << 16;
            }
        }

        return i;
    }
}
